Circuit breaker with ambient temperature compensation

ABSTRACT

The described circuit breakers will open an electrical circuit at a current level which remains substantially constant, independent of the ambient temperature variations. Each circuit breaker will be seen to incorporate a pair of temperature responsive bimetals selected of cross-sectional areas and temperature coefficients of expansion so as to maintain physical separations between them substantially constant in providing the desired current control.

United States Patent 1 Rhee [451 Dec. 17, 1974 1 1 CIRCUIT BREAKER WITH AMBIENT TEMPERATURE COMPENSATION [75] Inventor: Hackchan Rhee, Indianapolis, Ind.

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Oct. 23, 1973 [21] Appl. No.: 408,303

2,762,885 9/1956 Foster 337/101 3,165,609 1/1965 Norden 337/101 X 3,234,348 2/1966 Desio 337/10l-X 3,702,454 11/1972 Brown 337/101 X Primary Examiner-Arthur T. Grimley Attorney, Agent, or Firm--Eugene M. Whitacre; Mason DeCamillis 5 7] ABSTRACT The described circuit breakers will open an electrical circuit at a current level which remains substantially constant, independent of the ambient temperature variations. Each circuit breaker will be seen to incorporate a pair of temperature responsive bimetals selected of cross-sectional areas and temperature coefficients of expansion so as to maintain physical separations between them substantially constant in providing the desired current control.

3 Claims, 4 Drawing Figures PATENTEDBEEVIVI 71914 I CIRCUIT BREAKER WITH AMBIENT TEMPERATURE COMPENSATION FIELD OF THE INVENTION This invention relates to electrical circuit breakers, in general, and to such devices which operate substantially unaffected by variations in ambient temperature, in particular.

SUMMARY OF THE INVENTION As will become clear hereinafter, the circuit breakers of the present invention include a bimetallic strip through which current flows. When the level of current exceeds a predetermined magnitude, the deflection which the bimetal undergoes because of the heat generated separates a pair of electrical contacts to open the circuit path. Similar deflections of the bimetal as may result from ambient temperature increases can undesirably cause contact separation at lower current levels. In contradistinction to other circuit breaker constructions, this invention offsets these undesirable deflections in a manner other than by increasingly restraining the deflection of the bimetal as temperatures rise. As will be seen in the embodiments described below, such increases in ambient temperature as deflect the bimetal in a direction to open the circuit breaker will, at the same time, serve to maintain an arm retainer of the circuit breaker trip mechanism in substantially fixed relationship therewith so as to negate any such motion of the bimetal. That is, whereas other ambient temperature compensation schemes limit the undesired deflection of the bimetal, the arrangements of the instant case permit such deflection, but offset it before it can trip the breaker.

In one embodiment of the invention, a reversible expansion bimetal is affixed to the current sensing bimetal in a manner to deflect in the opposite direction as temperatures increase. The two bimetals are so selected and configured that the effects of temperature on one oppose the effects of temperature on the other, and keep substantially constant, an area of the reversibleexpansion bimetal which holds the arm retainer in place. In a second embodiment of the invention, the two bimetals deflect in the same direction, but the temperature compensating bimetal carries the arm retainer with it to maintain the fixed relationship between the trip mechanism and the current sensing bimetal.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the present invention will be more clearly understood from a consideration of the following description taken in connection with the accompanying drawings, in which:

FIGS. I and 1A shows a first embodiment ofa circuit breaker with ambient temperature compensation constructed in accordance with the present invention; and

FIGS. 2 and 2A show another embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring, now, to FIGS. 1 and 1A, the illustrated circuit breaker includes a housing 20, a cover 21, and a pin, or button, 22. A bi-metallic strip 23 is shown, conductively coupled by a braided copper wire 26 to sense the flow of current therein, and to deflect to the right,

as shown in the drawing, in response to the heat generated. The path for such current flow is through a conductive, upper ribbon spring 25, entering at a point 1, then through an upper electrical contact 30 to a lower electrical contact 31 affixed 'to a conductive, lower ribbon spring 24from there, through the wire 26 and the bimetal 23, to exit at the point 2. It will be readily apparent that the assembly of FIG. 1 represents the closed condition of the circuit breaker, in which the current path is via the contacts 30, 31 to electrically connect utilization apparatus coupled between points 1 and .2, although not so shown.

Also illustrated in FIGS. 1 and 1A are a second, reversible expansion bimetallic strip 33, an arm retainer of a trip mechanism 34, and a coil spring 35. The reversible bimetallic strip 33 is seamed to the lower bimetallic strip 23, as at point 3, and has an upper loop portion which rests atop the arm retainer 34, holding the upper ribbon spring 25 and the contacts 30, 31 in place. When the flow of current through the copper braid 2 6and, therefore, the current flow through the utilization apparatus connected between points 1 and 2-exceeds a predetermined level, the resulting deflection to the right of the metallic strip combination frees the arm retainer 34 from the previously restraining loop portion 100, to permit the ribbon spring 25 to deflect upwards, and separate the contacts 30, 31. This represents the open condition of the circuit breaker assembly. To reset the breaker after the fault condition has been corrected, the pin 22 is depressed until a first post 38 bears against the upper ribbon spring 25 sufficiently to move the retainer arm 34 beneath the restricting loop portion 100 of the reversible bimetallic strip 33. Electrical connection between the contacts 30, 31 is thereby once again established.

In one construction of the arrangement of FIGS. 1 and 1A, the contacts 30, 31 were selected of fine, silver-backed cadmium oxide alloy to withstand a 10,000 cycle test at an 8 ampere current level and a 50 cycle test at a 50 ampere level. In resetting, the pin 22 does not physically contact the bimetal, and the initial configuration of the bimetal is thus maintained. The configuration of the springs 24 and 25, together with the positioning of their contacts 30, 31, keeps those contacts open during the reset operation until the pin 22 is released. A second post 37 bears against the lower ribbon spring 24 on reset to also keep contacts 30, 31 separate, and to further cause them to come together by a sliding action which wipes their surfaces clean when pin 22 is released and moved upward by the coil spring 35. The relative positioning of these two springs 24, 25 is such that the force on the contacts 30, 31 when the breaker isclosed, the opening force of the upper spring 25, and the force on the contacts in resetting the breaker are all independent of the operation of the bimetal in sensing an over-current condition. Thus, any variation in spring force due to the vagaries of spring material selection or spring configuration will not affect the operation of the circuit breaker as long as the springs permit the resetting motion. At unusually high current levels, the braided copper wire 26 will burn to opencircuit the breaker prior to the damaging of any other part, such as the bimetal or the contacts 30, 31. The circuit breaker is thus designed to be quick acting and substantially free of product failures.

Additionally illustrated in FIG. 1 is the bimetal construction showing the seam welded segments 23, 33. At

a predetermined current level, the lower portion of the combination, 23, deflects to the right to free the loop portion 100 so as to release the arm retainer 34 and open-circuit the contacts 30, 31. The lower bimetal 23 is shown slotted-with the dimensions of the slot and the thickness and type of the bimetal .23 governing the current level at which sufficient deflection will result to release the arm retainer. The reversible bimetallic strip 33 is selected narrower than the bimetal 23 in order to reduce the rate of heat transfer from the bimetal 23 to the bimetal 33. This permits the bimetal 33 to deflect to the left at elevated ambient temperatures, to more than compensate any tendency of the bimetal 23 to deflect to the right due to such temperature conditions. The relative positioning of the loop 100 thereby remains unchanged with respect to the positioning of the arm retainer 34 as the ambient temperatures vary, permitting the circuit breaker assembly to continue to operate at substantially the same current levels, without being affected by ambient temperatures. The slot 35 in the arm retainer 34 upon which the loop 100 sits reduces the tendency for the circuit breaker to open at minor increases in current or ambient temperature.

The circuit breaker of FIGS. 2 and 2A also includes a housing 50, a cover 51, and a pin, or button, 52. A one-piece bimetallic strip 53 is shown, conductively coupled by a braided copper wire 56 to sense the flow of current therein, and to deflect to the right, as shown in the drawing, in response to the heat generated. The path for such current flow, as in FIGS. 1 and 1A, is through a conductive, upper ribbon spring 55, entering at a point 1], then through an upper electrical contact 60 to a lower electrical contact 61 affixed to a conductive, lower ribbon spring 64from there, through the wire 56 and the bimetal S3, to exit at the point 12. It will be readily apparent that the assembly of FIG. 2- like that of FIG. lrepresents the closed condition of the circuit breaker, in which the current path is via the contacts 60, 61 to electrically connect utilization apparatus coupled between points 11 and 12, although not so shown.

Also illustrated in FIGS. 2 and 2A are a second bimetallic strip 63, an arm retainer 64 of a trip mechanism, and a coil spring 70. The bimetallic strip 63 carries, at its uppermost end, the arm retainer 64 under an upper loop portion 102 of the bimetallic strip 53, while its lowermost end is affixed by a structural coupling 66. When the flow of current through the copper braid 56and, therefore, the current flow through the utilization apparatus connected between points 11 and l2exceeds a predetermined level, the resulting deflection to the right of the metallic strip 53 frees the arm retainer 64 from the previously restraining loop portion 102, to permit the ribbon spring 55 to deflect upward and separate the contacts 60, 61. This represents the open" condition of the circuit breaker assembly. To reset the breaker after the fault condition has been corrected, the pin 52 is depressed until a first post 68 bears against the top surface of the structural coupling 66 sufficiently to move the retainer arm 64 beneath the restricting loop portion 102 of the bimetallic strip 53. A second post 67 of pin 52 bears against the lower ribbon spring 64 during the reset operation to keep the contacts separate but to provide the sliding action between their surfaces when pin 52 is released and moved upwards by the coil spring 70. Electrical connection between the contacts 60, 61 is thereby established again, as in the embodiment of FIG. 1.

Protection against increases in ambient temperature as would affect the current level at which the bimetallic strip 53 will deflect to remove the restraint on the arm retainer 64 is provided in FIG. 2 by the bimetallic strip 63. Specifically, those increases in ambienttemperature as would tend to deflect the bimetal 53 to the right, affect the bimetal 63 in like manner, to move the arm retainer 64 in generally the same direction and amount as such temperature increases tend to deflect the bimetallic strip 53. The area of the arm retainer 64 thus covered and restrained by the loop 102 remains substantially unchanged as temperatures vary.

It will thus be seen that both the circuit breakers of FIGS. 1 and 2 provide temperature compensation by permitting the current sensing bimetallic strip to deflect as temperatures rise, and to provide a second, offsetting comparable deflection so that the trip mechanism remains substantially unaffected. Whereas the FIG. 1 construction employs a reversible expansion type bimetal to offset temperature induced deflections, the FIG. 2 embodiment employs a second bimetal to deflect the arm retainer in comparable ways. Each of these arrangements will thus be seen to be substantially different from previous circuit breaker designs where compensation was provided by increasing the tension imparted to the current sensing bimetal as temperatures increased. It will be readily apparent to'those skilled in the art that the designs of such tensioning schemes are much more critical to initiate than are the arrangements of the present invention, where all that is required is appropriate selection of the bimetallic elements and configuration employed.

While there has been described what are considered to be preferred embodiments of the present invention, it will be appreciated that changes may be made by those skilled in the art without departing from the scope of the teachings herein, of utilizing an additional bimetal to compensate the tendency of the current sensing bimetallic strip to open a circuit breaker at a reduced current level as ambient temperatures increase.

What is claimed is:

1. In a circuit breaker of the type including a pair of cooperating electrical contacts, an operating means for moving said contacts to their engaged and disengaged positions, responsive to a predetermined fault, an overload responsive trip means for sensing the occurrence of said predetermined fault and initiating movement of said operating means to the contact disengaged position, said trip means including a first bimetal in the current flow path of said circuit breaker and operative to deflect due to the heat generated thereby to actuate said operating means towards the contact disengaged position when the current flow reaches said predcter mined fault, and a housing for locating and enclosing the afore-mentioned circuit breaker components, the improvement therewith of:

a second bimetal within said housing, and proximately placed with respect to said, first bimetal to be substantially similarly affected thereas by variations in ambient temperature in said circuit breaker which tend to deflect said first bimetal independent of the current flow therethrough;

said second bimetal being also operative to deflect due to the heat generated by said variations in ambient temperature, but in a direction to oppose the actuation of said operating means towards the contact disengaged position caused by the deflection of said first bimetal as a result of said ambient temperature variations; with said first and second bimetals being selected of cross-sectional areas and temperature coefficients of expansion so as to maintain the physical separations between them substantially constant in the presence of ambient temperature changes;

whereby said operating means is actuated to the contact disengaged position upon the sensing of said same predetermined fault current flow, independent of ambient temperature conditions within said circuit breaker.

2. The combination of claim 1 wherein said operating means includes means retaining said contacts in electrical connection in the switch engaged position under the combined control of said first and second bimetals, and

wherein said first and second bimetals are axially aligned in opposing expansion direction to restrain movement of said electrical contact retaining means such that deflection of said first bimetal due to increases in ambient temperature are offset by the deflection of said second bimetal in opposite direction due to such temperature increases.

3. The combination of claim 1 wherein said operating means includes means retaining said contacts in electrical connection in the switch engaged position under the combined control of said first and second bimetals, and wherein said first and second bimetals are adjacently aligned, but in similar expansion "direction, to restrain movement of said electrical contact retaining means such that deflection of said first bimetal due to increases in ambient temperature are offset by the deflection of said second bimetal in the same direction due to such temperature increases.

Disclaimer 3,855,562.-Ha0lc0han Rhee, Indianapolis, Ind. CIRCUIT BREAKER WITH AMBIENT TEMPERATURE COMPENSATION. Patent dated. Dec. 17, 1974. Disclaimer filed May 26, 1977, by the assignee, BOA Oowpomtion. Hereby enters this disclamer to claims 1, 2 and 3 of said patent.

Disclaimer 3,855,562.Ha07c0han Rhee, Indianapolis, Ind. CIRCUIT BREAKER WITH AMBIENT TEMPERATURE COMPENSATION. Patent dated Dec. 17, 1974. Disclaimer filed May 26, 1977, by the assignee, ROA Uowpomtz'on. Hereby enters this disclamer to claims 1, 2 and 3 of said patent.

[Oficz'al Gazette July 26, 1.977.] 

1. In a circuit breaker of the type including a pair of cooperating electrical contacts, an operating means for moving said contacts to their engaged and disengaged positions, responsive to a predetermined fault, an overload responsive trip means for sensing the occurrence of said predetermined fault and initiating movement of said operating means to the contact disengaged position, said trip means including a first bimetal in the current flow path of said circuit breaker and operative to deflect due to the heat generated thereby to actuate said operating means towards the contact disengaged position when the current flow reaches said predetermined fault, and a housing for locating and enclosing the afore-mentioned circuit breaker components, the improvement therewith of: a second bimetal within said housing, and proximately placed with respect to said first bimetal to be substantially similarly affected thereas by variations in ambient temperature in said circuit breaker which tend to deflect said first bimetal independent of the current flow therethrough; said second bimetal being also operative to deflect due to the heat generated by said variations in ambient temperature, but in a direction to oppose the actuation of said operating means towards the contact disengaged position caused by the deflection of said first bimetal as a result of said ambient temperature variations; with said first and second bimetals being selected of crosssectional areas and temperature coefficients of expansion so as to maintain the physical separations between them substantially constant in the presence of ambient temperature changes; whereby said operating means is actuated to the contact disengaged position upon the sensing of said same predetermined fault current flow, independent of ambient temperature conditions within said circuit breaker.
 2. The combination of claim 1 wherein said operating means includes means retaining said contacts in electrical connection in the switch engaged position under the combined control of said first and second bimetals, and wherein said first and second bimetals are axially aligned in opposing expansion direction to restrain movement of said electrical contact retaining means such that deflection of said first bimetal due to increases in ambieNt temperature are offset by the deflection of said second bimetal in opposite direction due to such temperature increases.
 3. The combination of claim 1 wherein said operating means includes means retaining said contacts in electrical connection in the switch engaged position under the combined control of said first and second bimetals, and wherein said first and second bimetals are adjacently aligned, but in similar expansion direction, to restrain movement of said electrical contact retaining means such that deflection of said first bimetal due to increases in ambient temperature are offset by the deflection of said second bimetal in the same direction due to such temperature increases. 